In general, shortening the channel length of transistors serves to increase the operating speed of an electronic circuit such as a comparator. With the use of transistors having a small size, however, individual transistors end up having different characteristics due to manufacturing variation even among the transistors having the same structure and the same size. In the case of a comparator, such differences in transistor characteristics bring about an offset.
An analog-to-digital converter that is required to have high precision may employ the function to cancel an offset. Further, a decision-feedback equalizer used in a receiver circuit may readily perform equalization by use of a comparator having an offset cancellation function. Accordingly, it is preferable for a comparator to have an offset cancellation function.
A double-tail comparator includes an input stage and an output latch stage, and is capable of operating at high speed over a wide range of common voltage and power supply voltage. A double-tail comparator having an offset cancellation function is known in the art (see Patent Document 1, for example). A comparator that employs added adjustment-purpose transistors to cause the input transistors to have imbalance may suffer drop in operating speed due to the parasitic capacitance of the added transistors.